Machining systems are controlled by means of numerical control mechanisms, which are generally subdivided into three control units, an MMC operating system (Man Machine Communication) as data input and visualization unit, a PLC control unit (programmable logic controller) and an NC control unit. Data and control commands are input via the MMC operating system, are passed on to the NC control unit, are decoded in the NC control unit, and are separately further processed in accordance with geometric and technology data (NC control unit) and switching commands (PLC control unit). The NC and PCL control units transmit the actual machine state to the MMC control unit for visualization.
FIG. 1 shows a conventional machining system 1 which is controlled by means of a numerical control apparatus 2. On the hardware side, the control apparatus 2 comprises an MMC operating system 3 with a control computer 4, designed as an industrial PC, and an operating device 5 with a display 6 as display unit, and an input unit 7 which is designed for example in the form of a keyboard, mouse or touch panel. The control apparatus 2 furthermore comprises a machine control panel 8 for manual operation of the machining system 1, wherein mainly safety-relevant operations are performed, and an NCU assembly 9 (Numerical Control Unit) with integrated NC control unit 10 and PLC control unit 11. The NC and PLC control units 10, 11 can also be designed in the form of separate assemblies.
On the software side, the control apparatus 2 comprises an operating software 12 for controlling the machining system 1; software modules 13 for job management, tool management and pallet management; program management 14 for managing control programs; and a data storage 15 in which standard machining parameters for the control programs are stored. The term “control program” includes, in addition to the NC program, all technology data that is outsourced from the NC program to external data storages. Further applications, such as for example a construction system, a programming system or a combined construction and programming system, can moreover be installed on the control computer 4.
A design engineer, a programmer and a machine operator are involved in the production of a component on the machining system 1, which task can, however, also be performed in part in personal union by one or two persons. The component is constructed by means of a construction system 16 (CAD system) or a combined construction and programming system 17 (CAD-/CAM system), wherein the abbreviations CAD and CAM stand for Computer Aided Design and Computer Aided Manufacturing. Finished construction drawings are stored on a common CAD data storage 19 provided in a network 18 for this purpose, which CAD data storage can be accessed by the programmers when required.
The machining system 1 is controlled by control programs which are created by means of a programming system or manually on the operating device 5 of the MMC operating system 3. Programming systems know basic and special NC functions and know which technology data is required and which machining rules apply. Programming can therefore be automatically defined and a control program can be generated. In the embodiment shown in FIG. 1, in addition to the combined construction and programming system 17, one further combined construction and programming system 20 is installed on the control computer 4 and a programming system 21 (CAM system) is installed in the network 18. The programming systems 17, 20, 21 are connected to a CAM data storage 22 which can be accessed by the programmers and machine operators. The programmer stores the finished control programs in the CAM data storage 22. The machine operator can access the CAM data storage 22 and import the control programs from the CAM data storage 22 into the program management 14 of the control computer 4.
During programming, the programmer determines machining of a component. He/she determines which tools are used, the order of machining and which machining parameters apply, for example, for laser power and feed rate. Programming systems support the programmer in finding suitable machining parameters and machining strategies for his/her machining task. The information about suitable machining parameters and machining strategies is contained in so-called technology tables and sets of rules which define the data storage 15. Suitable machining parameters for all relevant values, which allow reliable machining, are stored in a technology table in dependence on the type of material, the material thickness and the machining method. If required, technology tables are defined in dependence on further parameters. For laser cutting, this includes, for example, the contour size which is subdivided into small, medium and large, and the machine type on which machining is to be performed.
The technology tables differentiate between general normally read-only technology tables of the machine manufacturer and customer-specific technology tables. General technology tables are determined by the machine manufacturer with great expense and are delivered to the customers together with the numerical control apparatus 2 of the machining system 1. Customer-specific technology tables can be created and changed by a programmer or machine operator. Machining parameters which are adapted to the machining tasks of a special client are stored in customer-specific technology tables. The machining parameters stored in the general technology tables are called “standard machining parameters” within the scope of this application.
For determining the standard machining parameters, machine manufacturers carry out uncountable parameter variations and evaluate the machining results. The decision about which machining parameters are stored in the technology table depends among others on the boundary conditions. When machining is to be performed with maximum machining quality, the machining parameters differ from those for machining with maximum speed. The machining parameters stated by the machine manufacturer in the general technology tables generally represent a compromise of different boundary conditions such as quality, process safety and speed. In general, the programmer and the machine operator do not know under which boundary conditions the machine manufacturer has determined the machining parameters of the general technology tables.
The properties of the material used have a considerable influence on the process safety of the machining process and the quality of the machining result. This can result in that machining parameters which have produced satisfactory machining results for a specific material, produce unsatisfactory machining results after change of the material supplier or when a different material charge is used, such that adjustment of the machining parameters is required.
FIG. 2 shows a conventional method for controlling a machining system by means of the control apparatus 2 shown in FIG. 1 in the form of a flow chart.
In step S1, the machine operator selects a control program that is stored in the program management 14 from the operating software 12 of the machining system 1. The control program refers to standard machining parameters which are stored in the data storage 15 on the control computer 4. The proposed standard machining parameters are transferred in step S2 from the data storage 15 into a storage 23 of the control computer 4 and are displayed on the display 6 of the operating device 5 in step S3.
In step S4, the machine operator decides whether he/she accepts the proposed standard machining parameters of the data storage 15 or whether changes are required. When the machine operator does not accept the proposed standard machining parameters (N in step S4), the machine operator changes the machining parameters in step S5. After step S5 or when the machine operator accepts the proposed standard machining parameters of the data storage 15 (J in step S4), the machining parameters are written from the storage 23 into a transmission file and stored in step S6. The machining parameters are thereby prepared in such a fashion that they can be read and processed by the NC control unit 10. In step S7, the control program is transferred from the control computer 4 to the NC control unit 10 and in step S8 the transfer file is transferred from the control computer 4 to the NC control unit 10. After step S8, the conventional method for controlling the machining system is terminated.
The adjustment of the machining parameters to changed boundary conditions requires programmers and/or machine operators with a great deal of experience, since the machining parameters depend on each other and moreover influence the machining process and the machining result in a non-linear way. Inexperienced programmers and machine operators face the great risk of changing the machining parameters in the wrong way. The time that an inexperienced machine operator requires for correctly changing the plurality of machining parameters can be very long and cause unnecessary cost due to the material used and the machine times.